Consumers use primary and rechargeable (secondary) batteries in portable electronic devices such as radios, compact disc players, cameras, cellular phones, electronic games, toys, pagers and computers devices. When the service run time of a primary battery is over, the battery is usually thrown away. The service run time of a typical primary battery generally only permits usage of between approximately 40 and 70% of the total battery storage capacity. Once that portion of the initial stored energy has been used, the battery generally cannot supply enough voltage to drive a typical electronic circuit. When the useful life of these batteries is spent, the consumers usually throw the batteries away even though the battery still contains between approximately 30 and 60% of its storage capacity. Thus, extending the service run time of a primary battery by allowing a safe deeper discharge will reduce waste by allowing the electronic devices to use more of the storage capacity of the battery before throwing it away.
The service run time of a rechargeable battery, however, is primarily dependent upon the number of and the efficiency of the charge cycles. Rechargeable batteries may be recharged and reused after each discharge cycle. As with a primary battery, after a percentage of the battery storage capacity has been used, the battery typically cannot supply enough voltage to drive an electronic circuit. Thus, each discharge cycle of a rechargeable battery may be extended if a deeper discharge of the battery is provided. The level of discharge of a rechargeable battery, however, has an impact on the number of and the efficiency of future charges of the rechargeable battery. In a Nickel Cadmium ("NiCd") battery, for example, a deep discharge is preferred because the battery may otherwise develop a "memory" effect if the battery is charged without being appropriately depleted resulting in a decreased capacity available for future charges decreases. Deep discharge of a lithium battery, however, may damage the electrochemical cells. The service run time of a rechargeable battery may generally be extended by efficiently controlling the discharge and charge cycles of the particular cell such that the total number of charge cycles may be maximized and the amount of energy recovered from each discharge cycle of the electrochemical cell is also optimized.
Present power controllers lack the ability to control multiple single-cell batteries or a multiple-cell battery on a cell-by cell basis. Some electronic devices that require multiple single-cell batteries or a multiple-cell battery, and some multiple-cell batteries, for example, have built-in controllers that stabilize the total output voltage of all of the cells, monitor the state of charge of all the cells together, or control the total charge of all the rechargeable cells together. Thus, the power controllers control multiple electrochemical cells together.
Each single-cell battery and each cell in a multiple-cell battery varies from the other cells even if the cells are the same type of electrochemical cell. These variations can cause problems in devices that require multiple single-cell batteries or multiple-cell batteries where one or more of the cells varies in electrochemical characteristics from the other cells in the battery. In addition, if a consumer replaces only a portion of the single-cell batteries in the device, some of the cells may have widely varying charge levels. As soon as one of these cells is discharged below a 100% level, the entire battery may fail and/or produce unsafe usage conditions.
In rechargeable batteries, varying charge levels among the cells can have much more drastic effects. If the consumer attempts to recharge a multiple single cell batteries or a multiple-cell battery that failed because one of the electrochemical, cells was weak and at least one of the remaining cells is fully charged, an overcharging condition of the cells could permanently damage the one or more of the cells or may even cause an explosion. In order to avoid this type of problem, however, designers have provided elaborate control schemes in an attempt to ensure that each electrochemical cell is charged to the same level as the other electrochemical cells and overall safety is not compromised. These schemes, however, still lack the ability to directly control each individual cell of the battery and cannot compensate for inherent variations of each cell and overall safety is not compromised.
In addition, consumers constantly demand smaller and lighter portable electronic devices. One of the primary obstacles to making these devices smaller and lighter is the size and weight of the batteries required to power the devices. In fact, as the electronic circuits get faster and more complex, they typically require even more current than they did before, and, therefore, the demands on the batteries are even greater. Consumers, however, will not accept more powerful and miniaturized devices if the increased functionality and speed requires them to replace or recharge the batteries much more frequently. Thus, in order to build faster and more complex electronic devices without decreasing their useful life, the electronic devices need to use the batteries more efficiently or the batteries themselves need to provide greater utilization of stored energy.
Some more expensive electronic devices include a voltage regulator circuit such as a switching converter (e.g., a DC/DC converter) in the devices for converting and/or stabilizing the output voltage of the battery. In these devices, multiple single-cell batteries are generally connected in series, and the total voltage of these batteries is converted into a voltage required by the load circuit by a converter. A converter can extend the run time of a primary battery, for example, by stepping down the battery output voltage in the initial portion of the battery discharge cycle where the battery would otherwise supply more voltage, and therefore more power, than the load circuit requires, and/or by stepping up the battery output voltage in the latter portion of the battery discharge where the battery would otherwise be exhausted because the output voltage is less than the load circuit requires.
The approach of having the converter in the electronic device, however, has several drawbacks. First, the converters are relatively expensive to place in the electronic devices because every device manufacturer has specific circuit designs that are made in a relatively limited quantity and, thus, have a higher individual cost. Second, battery suppliers have no control over the type of converter that will be used with a particular battery. Therefore, the converters are not designed to take advantage of the specific electrochemical properties of each type of electrochemical cell. Third, different types of primary and rechargeable electrochemical cells such as alkaline and lithium cells have different electrochemical properties and nominal voltages and, therefore, cannot be readily interchanged. Additionally, the converters take up valuable space in the electronic devices. Also, some electronic devices may use linear regulators instead of more efficient switching converters such as a DC/DC converter. In addition, electronic devices containing switching converters may create electromagnetic interference (EMI) that may adversely affect adjacent circuitry in the electronic device such as a radio frequency (RF) transmitter. By placing the converter in the battery, however, the source of the EMI can be placed farther away from other EMI sensitive electronics and/or could be shielded by a conductive container of the battery.
Another problem with present voltage converters is that they typically need multiple electrochemical cells, especially with respect to alkaline, zinc-carbon, nickel cadmium (NiCd) and silver oxide batteries, in order to provide enough voltage to drive the converter. In order to avoid this problem, present converters usually require multiple electrochemical cells connected in series to provide enough voltage to drive the converter, which may then step the voltage down to a level required by the electronic device. Thus, due to the converter's input voltage requirements, the electronic device must contain several electrochemical cells, even though the electronic device itself may only require a single cell to operate. This results in wasted space and weight and prevents further miniaturization of the electronic devices.
Other types of cells, such as metal-air cells, require a closely controlled environment of the electrochemical reaction to maximize the service run time of the cell. Some metal-air cell designs use mechanical valves to regulate the air flow into and out of the cell.
Thus, it would be advantageous to provide a single-cell battery having a built-in controller or a multiple-cell battery that has a built-in controller in each cell in order to provide control of the varying electrochemical properties or states of each individual electrochemical cell.
Thus, a need exists to optimally use the stored charge of a rechargeable battery before charging the battery in order to maximize its service run time. By designing batteries to provide a greater utilization of their stored energy, electronic devices can also use smaller or fewer batteries in order to further miniaturize portable electronic devices.